# Definition of Hermitian Operator in Dirac Notation

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In summary, a Hermitian operator is a mathematical construct used in quantum mechanics to represent physical observables. It is equal to its own conjugate transpose and is denoted by a hat symbol in Dirac notation. Hermitian operators are important in quantum mechanics as they correspond to measurable quantities and have real eigenvalues. They are also related to quantum states, with their eigenvalues representing possible outcomes of measurements and eigenvectors representing the state in which the measurement will yield that specific outcome. However, not all operators in quantum mechanics are Hermitian, as only those representing physical observables have this property.
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## Homework Statement

Using Dirac notation (bra, kets), define the meaning of the term "Hermitian".

## The Attempt at a Solution

From what I understand, a hermitian operator is simply one that has the same effect as its hermitian adjoint. So, I'm assuming it should simply be,

$<\psi|\hat{Q}|\psi>=<\psi|\hat{Q}^*|\psi>$

I've seen it written in more complicating ways, so I'm guessing there's a little more to it. Please help.

## 1. What is a Hermitian operator?

A Hermitian operator is a mathematical construct used in quantum mechanics to represent physical observables, such as position, momentum, and energy. It is defined as an operator that is equal to its own conjugate transpose, meaning the operator and its adjoint are the same.

## 2. How is a Hermitian operator written in Dirac notation?

In Dirac notation, a Hermitian operator is denoted by a hat symbol (^) above the operator, such as ̂A. The Hermitian adjoint of this operator is written as Â†.

## 3. What is the importance of Hermitian operators in quantum mechanics?

Hermitian operators play a crucial role in quantum mechanics as they represent physical observables, which are measurable quantities in the quantum world. They also have the special property of having real eigenvalues, which correspond to the possible outcomes of measurements.

## 4. How are Hermitian operators related to quantum states?

In quantum mechanics, Hermitian operators act on quantum states to produce a new quantum state. The eigenvalues of the operator correspond to the possible outcomes of measurements on the quantum state, and the eigenvectors of the operator represent the state in which the measurement will yield that specific outcome.

## 5. Can all operators in quantum mechanics be Hermitian?

No, not all operators in quantum mechanics are Hermitian. Only operators that represent physical observables, such as position, momentum, and energy, are Hermitian. Other operators, such as the time evolution operator, are not Hermitian but still play important roles in quantum mechanics.

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